Catalytic converters have been widely utilized with internal combustion engines, typically gasoline powered engines. In operation an oxidizing catalytic converter comprises a post combuster through which emissions from the internal combustion process are directed. The catalyst promotes the conversion of carbon monoxides and hydrocarbons in the emissions to carbon dioxide and water vapor.
In a typical application, the catalytic converter is located in the exhaust system as close to the exhaust engine manifold as practical. In this manner, advantage is taken of available heat in the exhaust gases to minimize the time lag in reaching the desired operating (reaction) temperature. The typical catalyst is a noble metal such as platinum or palladium.
As indicated above, typically catalytic converters have been utilized with gasoline powered internal combustion engines, rather than diesel engines such as truck engines. There are numerous reasons for this. For example, trucks typically have very limited space for the placement of catalytic equipment in the exhaust system. The largest space available is occupied by the muffler, leaving little if any room for effective placement of a catalytic converter. It is not generally reasonable to reduce the size of the muffler to allow for placement of a converter assembly. This is because reduction in the size of the muffler will generally lead to less sound attenuation and higher backpressure.
In addition, in a diesel powered truck system the acceptable amount of resistance to flow in the exhaust stream is strictly limited. More specifically, an effective muffler system for a diesel engine truck typically provides a backpressure close to the maximum backpressure allowable for efficient engine use. The added backpressure which would be introduced by placement of a conventional catalytic converter arrangement in the exhaust stream (in addition to the conventional muffler) would typically be unacceptably close to (if not over) the maximum backpressure allowable and would reduce fuel efficiency.
Nevertheless, there are reasons why it may be desirable to introduce a catalytic converter into a diesel exhaust flow stream. In particular, the catalyst allows for the oxidation of hydrocarbons in the gaseous phase, thereby reducing the concentration of hydrocarbons in the exhaust stream. Due to the concentration reduction, a lower amount of hydrocarbons would be adsorbed onto the surface of carbonaceous particles or soot in the stream. Thus there will be a mass reduction in the tailpipe emissions, if a catalytic converter can be efficiently utilized.